Electronic devices made with electron transport and/or anti-quenching layers

ABSTRACT

The present invention is directed to a photoactive device comprising an anode, a cathode, and a photoactive layer, which device further comprises an electron transport and/or anti-quenching layer which minimizes both electron transfer quenching and energy transfer quenching of the photoactive layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 10/612,482filed Jul. 2, 2003 which claims priority from U.S. ProvisionalApplication Ser. No. 60/394,767, filed Jul. 10, 2002, and U.S.Provisional Application Ser. No. 60/458,277, filed Mar. 28, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to photoactive electronic devices in whichthere is at least one active layer comprising an electron transportand/or anti-quenching composition.

2. Description of the Related Art

In organic photoactive electronic devices, such as light-emitting diodes(“OLED”), that make up OLED displays, the organic active layer issandwiched between two electrical contact layers in an OLED display. Inan OLED the organic photoactive layer emits light through thelight-transmitting electrical contact layer upon application of avoltage across the electrical contact layers.

It is well known to use organic electroluminescent compounds as theactive component in light-emitting diodes. Simple organic molecules,conjugated polymers, and organometallic complexes have been used.

Devices which use photoactive materials, frequently include one or morecharge transport layers, which are positioned between the photoactive(e.g., light-emitting) layer and one of the contact layers. A holetransport layer may be positioned between the photoactive layer and thehole-injecting contact layer, also called the anode. An electrontransport layer may be positioned between the photoactive layer and theelectron-injecting contact layer, also called the cathode.

When organometallic compounds, such as Ir and Pt complexes, are used asthe electroluminescent layer, a blocking layer inserted next to theluminescent layer on the cathode side can enhance the device efficiency2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (known as BCP or DDPA) wasused by Baldo et al. for this purpose. It was proposed that the BCPlayer functions as an “exciton blocker” to prevent the transfer of theenergy of a luminescent exciton to the adjacent layer. The blockinglayer is characterized by a band gap greater than the energy level ofexcitons formed in the luminescent layer.

U.S. Pat. No. 6,097,147 claims a light emitting device comprising: asubstantially transparent anode; a hole transporting layer over saidanode; an emission layer over said hole transporting layer; a blockinglayer over said emission layer; an electron transporting layer over saidblocking layer; and a cathode in electrical contact with said electrontransporting layer. It further claims a device wherein said blockinglayer is characterized by a band gap greater than the energy level ofexcitons formed in said emission layer.

However, energy transfer from photoactive materials to an adjacent layercan be quenched not only by energy transfer but also by electrontransfer to the adjacent layer, so the use of larger band gap excitonblocker is insufficient. Materials that can prevent both energy transferquenching and electron transfer quenching are needed.

SUMMARY OF THE INVENTION

The present invention is directed to a photoactive device comprising ananode, a cathode, and a photoactive layer, which device furthercomprises an electron transport and/or anti-quenching layer whichminimizes both electron transfer quenching and energy transfer quenchingof the photoactive layer.

In one embodiment is a photoactive electronic device comprising:

(a) an anode;

(b) a cathode, said cathode having a work function energy level E₃;

(c) a photoactive layer positioned between said anode and said cathode,said photoactive layer comprising a cyclometallated complex of atransition metal, said cyclometalated complex having a LUMO energy levelE₂ and a HOMO energy level E₄; and

(d) an electron transport and/or anti-quenching layer positioned betweensaid cathode and said photoactive layer, said electron transport and/oranti-quenching layer having a LUMO energy level E₁ and a HOMO energylevel E₅,

with the proviso that:E ₁ −E ₃<1V,  (1)E ₁ −E ₂>−1V, and  (2)E ₄ −E ₅>−1V.  (3)

As used herein, the term “charge transport composition” is intended tomean material that can receive a charge from an electrode andfacilitates movement through the thickness of the material withrelatively high efficiency and small loss of charge. Hole transportcompositions are capable of receiving a positive charge from an anodeand transporting it. Electron transport compositions are capable ofreceiving a negative charge from a cathode and transporting it. The term“anti-quenching composition” is intended to mean a material whichprevents, retards, or diminishes both the transfer of energy and thetransfer of an electron to/or from the excited state of the photoactivelayer to an adjacent layer. The term “photoactive” refers to anymaterial that exhibits electroluminescence, photoluminescence, and/orphotosensitivity. The term “HOMO” refers to the highest occupiedmolecular orbital of a compound. The term “LUMO” refers to the lowestunoccupied molecular orbital of a compound. The term “group” is intendedto mean a part of a compound, such as a substituent in an organiccompound. The prefix “hetero” indicates that one or more carbon atomshas been replaced with a different atom. The term “alkyl” is intended tomean a group derived from an aliphatic hydrocarbon having one point ofattachment, which group may be unsubstituted or substituted. The term“heteroalkyl” is intended to mean a group derived from an aliphatichydrocarbon having at least one heteroatom and having one point ofattachment, which group may be unsubstituted or substituted. The term“alkylene” is intended to mean a group derived from an aliphatichydrocarbon and having two or more points of attachment. The term“heteroalkylene” is intended to mean a group derived from an aliphatichydrocarbon having at least one heteroatom and having two or more pointsof attachment. The term “alkenyl” is intended to mean a group derivedfrom a hydrocarbon having one or more carbon-carbon double bonds andhaving one point of attachment, which group may be unsubstituted orsubstituted. The term “alkynyl” is intended to mean a group derived froma hydrocarbon having one or more carbon-carbon triple bonds and havingone point of attachment, which group may be unsubstituted orsubstituted. The term “alkenylene” is intended to mean a group derivedfrom a hydrocarbon having one or more carbon-carbon double bonds andhaving two or more points of attachment, which group may beunsubstituted or substituted. The term “alkynylene” is intended to meana group derived from a hydrocarbon having one or more carbon-carbontriple bonds and having two or more points of attachment, which groupmay be unsubstituted or substituted. The terms “heteroalkenyl”,“heteroalkenylene”, “heteroalkynyl” and “heteroalkynlene” are intendedto mean analogous groups having one or more heteroatoms. The term “aryl”is intended to mean a group derived from an aromatic hydrocarbon havingone point of attachment, which group may be unsubstituted orsubstituted. The term “heteroaryl” is intended to mean a group derivedfrom an aromatic group having at least one heteroatom and having onepoint of attachment, which group may be unsubstituted or substituted.The term “arylalkylene” is intended to mean a group derived from analkyl group having an aryl substituent, which group may be furtherunsubstituted or substituted. The term “heteroarylalkylene” is intendedto mean a group derived from an alkyl group having a heteroarylsubstituent, which group may be further unsubstituted or substituted.The term “arylene” is intended to mean a group derived from an aromatichydrocarbon having two points of attachment, which group may beunsubstituted or substituted. The term “heteroarylene” is intended tomean a group derived from an aromatic group having at least oneheteroatom and having two points of attachment, which group may beunsubstituted or substituted. The term “arylenealkylene” is intended tomean a group having both aryl and alkyl groups and having one point ofattachment on an aryl group and one point of attachment on an alkylgroup. The term “heteroarylenealkylene” is intended to mean a grouphaving both aryl and alkyl groups and having one point of attachment onan aryl group and one point of attachment on an alkyl group, and inwhich there is at least one heteroatom. Unless otherwise indicated, allgroups can be unsubstituted or substituted. The phrase “adjacent to,”when used to refer to layers in a device, does not necessarily mean thatone layer is immediately next to another layer. On the other hand, thephrase “adjacent R groups.” is used to refer to R groups that are nextto each other in a chemical formula (i.e., R groups that are on atomsjoined by a bond). The term “compound” is intended to mean anelectrically uncharged substance made up of molecules that furtherconsist of atoms, wherein the atoms cannot be separated by physicalmeans. The term “ligand” is intended to mean a molecule, ion, or atomthat is attached to the coordination sphere of a metallic ion. The term“complex”, when used as a noun, is intended to mean a compound having atleast one metallic ion and at least one ligand. The term“cyclometallated complex” is intended to mean a complex in which anorganic ligand is bound to a metal in at least two positions to form acyclic metal ligand structure, and in which at least one point ofattachment is a metal-carbon bond. In addition, the IUPAC numberingsystem is used throughout, where the groups from the Periodic Table arenumbered from left to right as 1 through 18 (CRC Handbook of Chemistryand Physics, 81^(st) Edition, 2000).

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Unless otherwise defined, allletter symbols in the figures represent atoms with that atomicabbreviation. Although methods and materials similar or equivalent tothose described herein can be used in the practice or testing of thepresent invention, suitable methods and materials are described below.All publications, patent applications, patents, and other referencesmentioned herein are incorporated by reference in their entirety. Incase of conflict, the present specification, including definitions, willcontrol. In addition, the materials, methods, and examples areillustrative only and not intended to be limiting.

Other features and advantages of the invention will be apparent from thefollowing detailed description, and from the claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a light-emitting diode (LED).

FIG. 2 is a schematic diagram of the energy levels in an LED.

FIG. 3 shows Formulae I(a) through I(e) for electroluminescent iridiumcomplexes.

FIG. 4 shows Formula II for an electron transport composition.

FIG. 5 shows Formulae II(a) through II(i) for an electron transportcomposition.

FIG. 6 shows Formulae III(a) and III(b) for an electron transportcomposition.

FIG. 7 shows Formulae IV(a) through IV(h) for a multidentate linkinggroup.

FIG. 8 shows Formula IV for an electron transport composition.

FIG. 9 shows Formulae IV(a) through IV(ag) for an electron transportcomposition.

FIG. 10 shows Formula shows Formula VI for an electron transportcomposition.

FIG. 11 shows Formulae VI(a) through VI(m) for an electron transportcomposition.

FIG. 12 shows Formula VII for an electron transport composition.

FIG. 13 shows formulae for known electron transport compositions.

FIG. 14 is a schematic diagram of a testing device for an LED.

FIG. 15 is a diagram of EL efficiency for devices using iridium complexI(a).

FIG. 16 is a diagram of EL efficiency for devices using iridium complexI(b).

FIG. 17 is a plot showing the best ET/AQ compositions for differentiridium complex emitters.

FIG. 18 is a plot of the LUMO of the iridium complex emitters vs theLUMO of ET/AQ compositions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to an electronic device comprising atleast one electron transport and/or anti-quenching layer and aphotoactive layer positioned between two electrodes. The device 100,shown in FIG. 1, has an anode layer 110 and a cathode layer 160.Adjacent to the anode is a layer 120 comprising hole transport material.Adjacent to the cathode is a layer 140 comprising an electron transportand/or anti-quenching material. Between the hole transport layer and theelectron transport and/or anti-quenching layer is the photoactive layer130. As an option, devices frequently use another electron transportlayer 150, next to the cathode. Layers 120, 130, 140, and 150 areindividually and collectively referred to as the active layers.

Depending upon the application of the device 100, the photoactive layer130 can be a light-emitting layer that is activated by an appliedvoltage (such as in a light-emitting diode or light-emittingelectrochemical cell), a layer of material that responds to radiantenergy and generates a signal with or without an applied bias voltage(such as in a photodetector). Examples of photodetectors includephotoconductive cells, photoresistors, photoswitches, phototransistors,and phototubes, and photovoltaic cells, as these terms are described inMarkus, John, Electronics and Nucleonics Dictionary, 470 and 476(McGraw-Hill, Inc. 1966). A device within the scope of this inventionshall mean a light-emitting diode, light-emitting electroluminescentdevice, or a photodetector as defined above.

FIG. 2 shows the schematics of the energetics of the devices, which willbe used for the discussion below. All of the energy levels arereferenced to the vacuum level, 117, with an energy defined to be zero.As such, they are all negative numbers. The lowest un-occupied molecularorbital (LUMO) energy level of the ET/AQ layer is defined as E₁. TheLUMO of the photoactive layer is defined as E₂. The work function of thecathode is defined as E₃, the highest occupied molecular orbital (HOMO)of the photoactive layer is defined as E₄, and the HOMO of the ET/AQlayer is defined as E₅. Higher energy means the energy level is closerto the vacuum level. These energy levels can be measured in the solidstate by techniques such as photoelectron spectroscopy. One can also usecyclic voltammetry measurement in solution to measure the relativeenergy levels of the molecule.

An effective electron transport and/or anti-quenching (ET/AQ) materialin an electroluminescent device has to possess the following properties.

1. The material has to be able to transport electrons efficiently,preferably with a mobility of >10⁻⁷ cm²/(V·sec).

2. The energy difference between the LUMO of the ET/AQ material and thework function of the cathode has to be small enough to allow efficientelectron injection from the cathode. The energy barrier is preferred tobe less than 1 V, that is, E₁−E₃<1 V

3. The LUMO level of ET/AQ has to be high enough to prevent it fromreceiving an electron from the photoactive layer. This usually requiresE₁−E₂>−1V. Preferably, E₁−E₂>0.

4. The HOMO level of ET/AQ has to be low enough to prevent it fromdonating an electron to the photoactive layer. This usually requiresE₄−E₅>−1V. Preferably, E₄−E₅>0.

Optimal energy level of ET/AQ in criteria 3 and 4 described above can bedetermined by the application of electron transfer theory. The rate ofelectron transfer reaction as a function of the energy difference isdescribed by the Marcus theory. (R. A. Marcus, P, Siders, J. Phys.Chem., 86, 622 (1982). In its simplest form, it is written ask=νexp[−(E _(f) −E _(i)+λ)²/4λk _(B) T]  (1)Here, k is the rate constant, k_(B) the Boltzman constant, T thetemperature, E_(i) and E_(f) are the energies of the initial and finalstates, and λ called the reorganization energy, is a phenomenologicalparameter describing the collective effects of the vibronic interactionsin the initial and final states. The pre-factor ν involves wave functionoverlap integrals, α, and is phenomenologically characterized asdepending on the charge separation distance r viaν(r)=ν₀exp[−α(r−r ₀)]  (2)The prefactor ν₀ tends to be universally about 10⁻¹³ sec⁻¹.

The energy of the final state, that is, the charge separated state,depends on the separation distance of the electron and hole, r, as wellas the applied electric field, E₀. It can be written asE _(f) =E _(f) ^(∞) −e ²/(∈r)−E ₀ z  (3)where E_(f) ^(∞) is the energy of the charge separated state in theabsence of an external field and with infinite separation of theelectron and hole, ∈ is the dielectric constant of the medium, and z isthe direction of the applied field. How to calculate the electrontransfer rate under applied field and variable electron hole distancehas been discussed before by Wang and Suna, J. Phys. Chem., 101,5627-5638 (1997).

In criteria 3, to prevent significant electron transfer quenching tooccur, the LUMO level of the ET/AQ layer has to be high enough such thatthe electron transfer rate from the photoactive layer to the ET/AQ layeris significantly less than the excited state radiative decay rate of theexciton. So the optimal location of the LUMO level depends on thereorganization energy λ and overlap integral α of the electron transferreaction involved, and the radiative lifetime of the exciton of thephotoactive layer. Typically, this requires E₁−E₂>−1V. Preferably,E₁−E₂>0.

In criteria 4, similarly, the HOMO level of the ET/AQ layer has to below enough such that the electron transfer rate from the ET/AQ layer tothe luminescent layer is significantly less than the excited stateradiative decay rate of the exciton. The optimal location of the HOMOlevel depends on the reorganization energy λ and overlap integral α ofthe electron transfer reaction involved, and the radiative lifetime ofthe exciton of the photoactive layer. This usually requires E₄−E₅>−1V.Preferably, E₄−E₅>0.

For any given photoactive material, there is therefore an optimal ET/AQmaterial to use which fulfills the requirement outlined in criteria 1 to4. For a series of structurally similar ET/AQ materials, where thereorganization energy and overlap integral are expected to be similar,one expects to find a correlation between the efficiency of the deviceand the LUMO energy of the ET/AQ material. For a given photoactivematerial, there should be an optimal range of the LUMO energies of ET/AQmaterial where the maximal efficiency is achieved.

It is also to be understood that the ET/AQ material has to be chemicallycompatible with the photoactive material used. For example, the ET/AQmaterial has to form a smooth film when deposited on the photoactivematerial layer. If aggregation occurs, the performance of the devicewill deteriorate. The occurrence of aggregation can be detected byvarious known techniques in microscopy and spectroscopy.

The other layers in the device can be made of any materials which areknown to be useful in such layers. The anode 110, is an electrode thatis particularly efficient for injecting positive charge carriers. It canbe made of, for example materials containing a metal, mixed metal,alloy, metal oxide or mixed-metal oxide, or it can be a conductingpolymer, and mixtures thereof. Suitable metals include the Group 11metals, the metals in Groups 4, 5, and 6, and the Group 8-10 transitionmetals. If the anode is to be light-transmitting, mixed-metal oxides ofGroups 12, 13 and 14 metals, such as indium-tin-oxide, are generallyused. The anode 110 may also comprise an organic material such aspolyaniline as described in “Flexible light-emitting diodes made fromsoluble conducting polymer,” Nature vol. 357, pp 477-479 (11 Jun. 1992).At least one of the anode and cathode should be at least partiallytransparent to allow the generated light to be observed.

Examples of hole transport materials which may be used for layer 120have been summarized, for example, in Kirk-Othmer Encyclopedia ofChemical Technology, Fourth Edition, Vol. 18, p. 837-860, 1996, by Y.Wang. Both hole transporting molecules and polymers can be used. Thecompound bis(4-N,N-diethylamino-2-methylphenyl)-4-methylphenylmethane(MPMP) has been disclosed to be a suitable hole transport composition inPetrov et al., Published PCT application WO 02/02714. Commonly used holetransporting molecules are:N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine(TPD), 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC),N,N′-bis(4-methylphenyl)-N,N′-bis(4-ethylphenyl)-[1,1′-(3,3′-dimethyl)biphenyl]-4,4′-diamine(ETPD), tetrakis-(3-methylphenyl)-N,N,N′,N′-2,5-phenylenediamine (PDA),a-phenyl-4-N,N-diphenylaminostyrene (TPS), p-(diethylamino)benzaldehydediphenylhydrazone (DEH), triphenylamine (TPA),bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylphenyl)methane (MPMP),1-phenyl-3-[p-(diethylamino)styryl]-5-[p-(diethylamino)phenyl]pyrazoline(PPR or DEASP), 1,2-trans-bis(9H-carbazol-9-yl)cyclobutane (DCZB),N,N,N′,N′-tetrakis(4-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TTB),and porphyrinic compounds, such as copper phthalocyanine. Commonly usedhole transporting polymers are polyvinylcarbazole,(phenylmethyl)polysilane, and polyaniline and mixtures thereof. It isalso possible to obtain hole transporting polymers by doping holetransporting molecules such as those mentioned above into polymers suchas polystyrene and polycarbonate.

Examples of the photoactive layer 130 include all knownelectroluminescent materials. Organometallic electroluminescentcompounds are preferred. The most preferred compounds includecyclometalated iridium and platinum electroluminescent compounds andmixtures thereof. Complexes of Iridium with phenylpyridine,phenylquinoline, or phenylpyrimidine ligands have been disclosed aselectroluminescent compounds in Petrov et al., Published PCT ApplicationWO 02/02714. Other organometallic complexes have been described in, forexample, published applications US 2001/0019782, EP 1191612, WO02/15645, and EP 1191614. Electroluminescent devices with an activelayer of polyvinyl carbazole (PVK) doped with metallic complexes ofiridium have been described by Burrows and Thompson in published PCTapplications WO 00/70655 and WO 01/41512. Electroluminescent emissivelayers comprising a charge carrying host material and a phosphorescentplatinum complex have been described by Thompson et al., in U.S. Pat.No. 6,303,238, Bradley et al., in Synth. Met. (2001), 116 (1-3),379-383, and Campbell et al., in Phys. Rev. B, Vol. 65 085210. as havebeen Examples of a few suitable iridium complexes are given in FIG. 3,as Formulae I(a) through I(e). Analogous tetradentate platinum complexescan also be used. These electroluminescent complexes can be used alone,or doped into charge-carrying hosts, as noted above.

One type of ET/AQ material is a phenanthroline derivative. Thephenanthroline derivative can have Formula II, shown in FIG. 4, wherein:

-   -   R¹ and R² are the same or different at each occurrence and are        selected from H, F, Cl, Br, alkyl, heteroalkyl, alkenyl,        alkynyl, aryl, heteroaryl, C_(n)H_(a)F_(b), OC_(n)H_(a)F_(b),        C₆H_(c)F_(d), and OC₆H_(c)F_(d);    -   a, b, c, and d are 0 or an integer such that a+b=2n+1, and        c+d=5,    -   n is an integer;    -   x is 0 or an integer from 1 through 3;    -   y is 0, 1 or 2;

with the proviso that there is at least one substituent on an aromaticgroup selected from F, C_(n)H_(a)F_(b), OC_(n)H_(a)F_(b), C₆H_(c)F_(d),and OC₆H_(c)F_(d). Specific examples of such phenanthrolines areFormulae II(a) through II(i) in FIG. 5.

The phenanthroline derivative can have Formulae III(a) or II(b), shownin FIG. 6, wherein:

-   -   R¹, R², a through d, n and x are as defined above;    -   R³ is the same or different at each occurrence and is selected        from a single bond and a group selected from alkylene,        heteroalkylene, arylene, heteroarylene, arylenealkylene, and        heteroarylenealkylene;    -   Q is selected from a single bond and a multivalent group;    -   m is an integer equal to at least 2; and    -   p is 0 or 1.        Examples of multivalent Q groups are shown as Formulae IV(a)        through IV(h) in FIG. 7.

Another type of ET/AQ material is a quinoxaline derivative. Thequinoxaline derivative can have Formula V, shown in FIG. 8, wherein:

-   -   R⁴ and R⁵ are the same or different at each occurrence and are        selected from H, F, Cl, Br, alkyl, heteroalkyl, alkenyl,        alkynyl, aryl, heteroaryl, alkylenearyl, alkenylaryl,        alkynylaryl, alkyleneheteroaryl, alkenylheteroaryl,        alkynylheteroaryl, C_(n)H_(a)F_(b), OC_(n)H_(a)F_(b),        C₆H_(c)F_(d), and OC₆H_(c)F_(d), or both of R⁵ together may        constitute an arylene or heteroarylene group;    -   a, b, c, and d are 0 or an integer such that a+b=2n+1, and        c+d=5,    -   n is an integer, and    -   w is 0 or an integer from 1 through 4.        Specific examples of quinoxalines of this formula are given as        Formulae V(a) through V(ag) in FIG. 9.

The quinoxaline can have Formula VI, shown in FIG. 10, wherein:

-   -   R⁴, R⁵, a through d, and n are as defined above,    -   R³ is the same or different at each occurrence and is selected        from a single bond and a group selected from alkylene,        heteroalkylene, arylene, heteroarylene, arylenealkylene, and        heteroarylenealkylene;    -   Q is selected from a single bond and a multivalent group;    -   m is an integer equal to at least 2;    -   p is 0 or 1; and    -   w is 0 or an integer from 1 through 4.        Examples of Q groups are discussed above. Specific examples of        quinoxalines of this formula are Formulae VI(a) through VI(m),        shown in FIG. 11.

The quinoxaline can have Formula VII, shown in FIG. 12, where R³, R⁴,R⁵, X, a through d, m, n, p and w are as defined above,

Examples of additional electron transport materials which can be used inlayer 150 include metal chelated oxinoid compounds, such astris(8-hydroxyquinolato)aluminum (Alq₃); and azole compounds such as2-(4-biphenylyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole (PBD) and3-(4-biphenylyl)-4-phenyl-5-(4-t-butylphenyl)-1,2,4-triazole (TAZ), andmixtures thereof.

The cathode 160, is an electrode that is particularly efficient forinjecting electrons or negative charge carriers. The cathode can be anymetal or nonmetal having a lower work function than the anode. Materialsfor the cathode can be selected from alkali metals of Group 1 (e.g., Li,Cs), the Group 2 (alkaline earth) metals, the Group 12 metals, includingthe rare earth elements and lanthamides, and the actinides. Materialssuch as aluminum, indium, calcium, barium, samarium and magnesium, aswell as combinations, can be used. Li-containing organometalliccompounds, LiF, and Li₂O can also be deposited between the organic layerand the cathode layer to lower the operating voltage.

It is known to have other layers in organic electronic devices. Forexample, there can be a layer (not shown) between the anode 110 and holetransport layer 120 to facilitate positive charge transport and/orband-gap matching of the layers, or to function as a protective layer.Layers that are known in the art can be used. In addition, any of theabove-described layers can be made of two or more layers. Alternatively,some or all of anode layer 110, the hole transport layer 120, theelectron transport layers 140 and 150, and cathode layer 160, may besurface treated to increase charge carrier transport efficiency. Thechoice of materials for each of the component layers is preferablydetermined by balancing the goals of providing a device with high deviceefficiency.

It is understood that each functional layer may be made up of more thanone layer.

The device can be prepared by a variety of techniques, includingsequentially vapor depositing the individual layers on a suitablesubstrate. Substrates such as glass and polymeric films can be used.Conventional vapor deposition techniques can be used, such as thermalevaporation, chemical vapor deposition, and the like. Alternatively, theorganic layers can be coated from solutions or dispersions in suitablesolvents, using any conventional coating or printing technique,including but not limited to spin-coating, dip-coating, roll-to-rolltechniques ink-jet printing, gravure printing, and screen printing. Ingeneral, the different layers will have the following range ofthicknesses: anode 110, 500-5000 Å, preferably 1000-2000 Å; holetransport layer 120, 50-2000 Å, preferably 200-1000 Å; photoactive layer130, 10-2000 Å, preferably 100-1000 Å; electron transport layer 140 and150, 50-2000 Å, preferably 100-1000 Å; cathode 160, 200-10000 Å,preferably 300-5000 Å. The location of the electron-hole recombinationzone in the device, and thus the emission spectrum of the device, can beaffected by the relative thickness of each layer. Thus the thickness ofthe electron-transport layer should be chosen so that the electron-holerecombination zone is in the light-emitting layer. The desired ratio oflayer thicknesses will depend on the exact nature of the materials used.

EXAMPLES

The following examples illustrate certain features and advantages of thepresent invention. They are intended to be illustrative of theinvention, but not limiting. All percentages are by weight, unlessotherwise indicated.

Examples 1-17

These examples illustrate the preparation of some ET/AQ compositions.

Example 1

This example illustrates the preparation of Compound V(b) in FIG. 9.

A mixture of 3,4-diaminotoluene (28.78 g, 0.236 mol) and benzil (45 g,0.214 mol) was refluxed in 738 ml chloroform with 2.16 mltrifluoroacetic acid for 3 hours. The mixture was washed 3 times with10% HCl, brine, and dried over MgSO₄, filtered, and then filteredthrough a silica bed with vacuum. The resultant solution was evaporatedto dryness. Recrystallized 69 grams of crude product from 550 mlmethanol. Filtered solids were dried in a vacuum oven at 50° C. for 1hour to yield 55.56 g of dried solid. 78.8% yield

Example 2

This example illustrates the preparation of Compound V(e) in FIG. 9.

A mixture of 3,4-diaminotoluene (4.49 g, 0.037 mol) and4,4′-dimethoxybenzil (9.46 g, 0.035 mol) was refluxed in 125 mlchloroform with 0.35 ml trifluoroacetic acid for 6 hours. The mixturewas washed 2 times with water, dried over MgSO₄, and evaporated to ˜11grams. The solid was dissolved in 1:1 ethyl acetate:chloroform for flashchromatography and eluted with ethyl acetate. Evaporated to 9.7 grams ofdark solid. 72% yield

Example 3

This example illustrates the preparation of Compound V(d) in FIG. 9.

A mixture of 3,4-diaminotoluene (5.36 g, 44 mmol) and phenanthrenequinone (8.33 g, 0.040 mol) was refluxed in 119 ml chloroform with 0.4ml trifluoroacetic acid for 6 hours. The mixture was filtered through amedium frit and recrystallized from 430 g of methyl ethyl ketone toyield 5.5 g fluffy wool-like, yellow product. 46% yield

Example 4

This example illustrates the preparation of Compound V(f) in FIG. 10.

A mixture of 3,4-diaminotoluene (5.36 g, 44 mmol) and 2,2′-Pyridil (8.49g, 40 mmol) was refluxed in 119 ml chloroform with 0.4 mltrifluoroacetic acid for 4 hours. The reaction mixture was separated andwashed 4 times with 100 ml water, and evaporated to 10.4 grams. Theresultant solid was dissolved in 1:1 ethyl acetate:chloroform for flashchromatography and eluted with ethyl acetate. Evaporated to yield 9.3grams of solid.

Example 5

This example illustrates the preparation of Compound V(g) in FIG. 10.

A mixture of methyl-3,4-diaminobenzoate (7.28 g, 44 mmol) and benzil(8.41 g, 40 mmol) was refluxed in 140 ml methylene chloride for 21hours. The reaction mixture was evaporated to dryness and then dissolvedin 520 ml methanol and 150 ml methylene chloride at reflux. The solutionwas then partially evaporated to selectively crystallize the desiredproduct

Example 6

This example illustrates the preparation of Compound V(k) in FIG. 10.

A mixture of Methyl-3,4-diaminobenzoate (6.37 g, 0.038 mol) and4,4′-dimethoxybenzil (9.46 g, 0.035 mol) was refluxed in 142 mlmethylene chloride with 3 drops trifluoroacetic acid for 5 hours. 10.7 gN-methylpyrrolidinone was added and reflux continued for 26 more hours.The mixture was washed 3 times with water, dried over MgSO₄, filteredand then precipitated the product be decanting the organic solution into550 g methanol. After standing overnight, the product was filtered anddried at 95° C. in vacuum to yield 10.39 g product.

Example 7

This example illustrates the preparation of Compound V(r) in FIG. 10.

A mixture of Methyl-3,4-diaminobenzoate (6.12 g, 0.037 mol) andphenanthrene quinone (7.08 g, 0.034 mol) was refluxed in 119 mlmethylene chloride. 100 grams of N-methylpyrrolidinone was added and thechlorinated solvent was distilled out. The pot was warmed to 150° C.whereupon a clear solution was obtained and the reaction was tracked bygas chromatography. The product was precipitated by pouring into 410 gmethanol and the solid precipitate filtered off. The product wasrecrystallized from toluene then recrystallized again from a combinationof methyl ethyl ketone 1200 g, toluene 150 g, and tetrahydrofuran 1100g. Yield was 3.3 grams of pearly golden wool-like material.

Example 8

This example illustrates the preparation of Compound V(I) in FIG. 10.

A mixture of 1,2-phenylenediamine (13.91 g, 0.129 mol) and4,4′-dibromobenzil (45, 0.116 mol) was refluxed in 558 ml chloroformwith 1.0 ml trifluoroacetic acid for 6 hours. The mixture was washed 3times with 10% HCl, and evaporated to ˜51 grams. Recrystallized from 600ml ethyl acetate with 100 ml methanol at reflux. Large crystals formedovernight and were filtered and washed with methanol twice and dried to29.63 g with a 4.9 g second crop from the chilled mother liquor.

Example 9

This example illustrates the preparation of Compound V(h) in FIG. 10.

A mixture of 2,3-diaminotoluene (4.84 g, 0.040 mol) and benzil (7.56 g,0.036 mol) was refluxed in 112 ml methylene chloride for 19 hours. Themixture was washed 4 times with 12% HCl, and dried over MgSO₄ filteredand evaporated to ˜9.5 grams of brown solid. The solid was dissolvedinto 495 g methanol at reflux and then ˜300 g solvent was distilled out.Cooling with ice yielded nice crystals. Filtered and washed crystal cakewith methanol.

Example 10

This example illustrates the preparation of Compound V(i) in FIG. 9.

A mixture of 2,3-diaminotoluene (5.05 g, 0.041 mol) andphenanthrenequinone (7.84 g, 0.38 mol) were refluxed in 112 mlchloroform for 29 hours. The resultant solution was chromatographed downa silica column with chloroform eluant. Evaporated product from solventto yield about 10 grams before vacuum oven drying. Material appearedcrystalline

Example 11

This example illustrates the preparation of Compound V(j) in FIG. 9.

A mixture of methyl-3,4-diaminobenzoate (7.28 g, 0.044 mol) and2,2′-pyridil (8.48 g, 0.040 mol) was refluxed in 140 ml methylenechloride for 7 hours. The solution was evaporated to 15.7 grams and thesolid dissolved in 240 ml methylene chloride and 140 ml methanol atreflux. After addition of 280 ml methanol and evaporation of ˜150 ml ofthe solvent the solution was left to stand overnight. The resultingsolid was collected and dried to 9.8 grams. Took 7.7 g material anddissolved in 203 g methanol with 50 g methylene chloride. Distilledoff >50 ml of solvent. Crystals formed overnight. Filtered and dried invacuum oven.

Example 12

This example illustrates the preparation of Compound VI(a) in FIG. 9.

A mixture of 3,3-diaminobenzidine (0.9458 g, 2.14 mmol) and1,10-phenanthroline-5,6-dione (0.9458 g, 4.5 mmol) were heated at 85° C.in 10 g n-methylpyrrolidinone with 0.045 ml trifluoroacetic acid for 23hours. At ambient temperature chloroform was charged to pot and contentswere filtered through a fine frit and washed with acetone, anddiethylether then dried at 90° C. and vacuum.

Example 13

This example illustrates the preparation of Compound II(c) in FIG. 5.

A mixture of 2,9-diiodo-1,10-phenanthroline (900 mg, 2.08 mmol, preparedaccording to: Toyota et al. Tetrahedron Letters 1998, 39, 2697-2700),3-trifluoromethylbenzeneboronic acid (989 mg, 5.20 mmol, AldrichChemical Company, Milwaukee, Wis.), tetrakistriphenylphosphine palladium(481 mg, 0.416 mmol, Aldrich Chemical Company), and sodium carbonate(882 mg, 8.32 mmol) were allowed to reflux in water (20 mL)/toluene (50mL) for 15 h under nitrogen. Then the organic layer was separated, andthe aqueous layer extracted with 3×25 mL of chloroform. The organiclayers were combined, dried with sodium sulfate, and evaporated todryness. Purification was accomplished by silica gel flashchromatography with hexanes/dichloromethane (1:1, v:v) as the eluent(product R_(f)=0.25), to afford the desired product, >95% pure by ¹HNMR, as a pale yellow solid (560 mg, 57%). ¹H NMR (CDCl₃, 300 MHz, 296K): δ 8.81 (s, 2H), 8.63 (d, 2H, J=7.5 Hz), 8.36 (d, 2H, J=8.4 Hz), 8.19(d, 2H, J=8.41 Hz), 7.84 (s, 2H), 7.68-7.77 (m, 6H) ppm. ¹⁹F NMR (CDCl₃,282 MHz, 296 K) δ −63.25 ppm.

Compounds II(a), II(g), II(h) and II(i) were made using an analogousprocedure.

Example 14

This example illustrates the preparation of Compound II(b) in FIG. 5.

The same procedure was used as in Example 13, with3,8-dibromo-1,10-phenanthroline (1.5 g, 4.4 mmol, prepared according to:Saitoh et al. Canadian Journal of Chemistry 1997, 75, 1336-1339.),4-trifluoromethylbenzeneboronic acid (2.11 g, 11.1 mmol, LancasterChemical Company, Windham, N.H.), tetrakistriphenylphosphine palladium(513 mg, 0.444 mmol), and sodium carbonate (1.41 g, 13.3 mmol), water(20 mL), and toluene (100 mL). Purification was achieved via silica gelflash chromatography (dichloromethane/methanol, 9:1 v:v), and then bywashing the product with cold methanol, to afford a white solid (520 mg,25%) >95% pure by ¹H NMR. ¹H NMR (CDCl₃, 300 MHz, 296 K): δ 9.46 (d, 2H,J=2.3 Hz), 8.45 (d, 2H, 2.3 Hz), 7.94 (s, 2H), 7.91 (d, 4H, J=8.3 Hz),7.82 (d, 4H, J=8.4 Hz) ppm. ¹⁹F NMR (CDCl3, 282 MHz, 296 K) δ −63.12ppm.

Example 15

This example illustrates the preparation of Compound II(e) in FIG. 5.

2,9-Diiodo-1,10-phenanthroline (1.00 g, 2.31 mmol),4-fluorobenzeneboronic acid (972 mg, 6.96 mmol),bis(diphenylphosphino)butane (92 mg, 0.23 mmol, Aldrich), palladiumacetate (52 mg, 0.23 mmol, Aldrich), and potassium fluoride (810 mg,13.9 mmol, Aldrich) were allowed to reflux in anhydrous dioxane (100 mL)for 15 h, after which time the dioxane was removed under reducedpressure, and the crude residue was subjected to an aqueous work-up asfor Example 1. Purification was achieved via silica gel flashchromatography (dichloromethane, 100% product R_(f)=0.57), to afford apale yellow solid (567 mg, 67%), >95% pure by ¹H NMR. ¹H NMR (CDCl₃, 300MHz, 296 K): δ 8.43 (dd, 4H, J_(HH)=10.4 Hz, J_(HF)=5.5 Hz), 8.28 (d,2H, J=8.4 Hz), 7.77 (s, 2H), 7.26 (dd, 4H, J_(HH)=9.9 Hz, J_(HF)=5.9 Hz)ppm. ¹⁹F NMR (CDCl3, 282 MHz, 296 K) δ −113.0 ppm.

Example 16

This example illustrates the preparation of Compound II(d) in FIG. 5.

The same procedure was used as in Examples 13 and 14, using4,7-dichloro-1,10-phenanthroline (300 mg, 1.20 mmol, prepared accordingto: J. Heterocyclic Chemistry 1983, 20, 681-6),3,5-bis(trifluoromethyl)benzeneboronic acid (0.930 mg, 3.60 mmol,Aldrich), bis(diphenylphosphino)butane (154 mg, 0.361 mmol), palladiumacetate (81 mg, 0.361 mmol), sodium carbonate (0.510 mg, 9.62 mmol),water (5 mL), and toluene (30 mL), to afford the desired product as awhite solid (410 mg, 56%). ¹H NMR (CDCl₃, 300 MHz, 296 K): δ 9.35 (d,2H, J=4.49 Hz), 8.06 (s, 2H), 8.00 (s, 4H), 7.73 (2H, s), 7.66 (d, 2H,J=4.52 Hz) ppm. ¹⁹F NMR (CDCl₃, 282 MHz, 296 K) δ −63.32 ppm.

Example 17

This example illustrates the preparation of Compound II(f) in FIG. 5.

The same procedure was used as in Example 15, using2,9-dichloro-phenanthroline (1.0 g, 4.01 mmol, prepared according to:Yamada et al. Bulletin of the Chemical Society of Japan 1990, 63,2710-12), 3,5-bistrifluoromethylbenzene-boronic acid (2.59 g, 10.0mmol), bis(diphenylphosphino)butane (171 mg, 0.401 mmol), palladiumacetate (90 mg, 0.401 mmol), and potassium fluoride (1.40 g, 24.1 mmol),and anhydrous dioxane (100 mL). The product was purified by washing thecrude material with diethyl ether, to afford the desired product as awhite solid (345 mg, 14%). ¹H NMR (CDCl₃, 300 MHz, 296 K): δ 8.92 (d,4H, J_(HF)=1.46 Hz), 8.45 (d, 2H, J=8.3 Hz), 8.25 (d, 2H, J=8.5 Hz),8.02 (s, 2H), 7.91 (s, 2H) ppm. ¹⁹F NMR (CDCl₃, 282 MHz, 296 K) δ −63.50ppm.

The properties of the electron transport and/or anti-quenchingcompositions are summarized in Table 1 below. Known ET/AQ compounds Aand B are shown in FIG. 13. TABLE 1 Properties Absorption AbsorptionLUMO vs onset (nm), maximum E_(1/2) vs SCE vacuum (eV), Compounds E1-E5(nm) (volt), E1 Compound 382 318 −1.56 −3.28 II(b) Compound 376 320−1.77 −3.07 II(a) Compound 368 342 −1.68 −3.16 II(c) Compound 362 310−1.54 −3.3 II(d) Compound 372 342 −1.8 −3.04 II(e) Compound 370 342−1.52 −3.32 II(f) Compound 375 345 −1.5 −3.33 V(a) Compound 378 339 −1.6−3.24 V(b) Compound 400 385 −1.17 −3.67 V(c) Compound 410 397 −1.3 −3.54V(d) Compound 390 352 −1.29 −3.55 V(g) Compound — — — — V(a) Compound405 369 −1.66 −3.18 V(e) Compound 378 339 −1.53 −3.31 V(f) Compound 420382 −1.35 −3.49 V(k) Compound 407 394 −1.28 −3.56 V(i) Compound 385 343−1.59 −3.25 V(h) Compound 417 401 −1.03 −3.81 V(r) Compound 380 347−1.49 −3.35 V(l) Compound 380 342 −1.22 −3.62 V(j) Comp. A 368 310 −1.85−2.99 DDPA Comp. B 366 316 −1.95 −2.89 DPA

Example 18

This example illustrates the preparation of an iridiumelectroluminescent complex, shown as Formula I(a) in FIG. 3.

Phenylpyridine ligand 2-(4-fluorophenyl)-5-trifluoromethylvpridine

The general procedure used was described in O. Lohse, P. Thevenin, E.Waldvogel Synlett, 1999, 45-48. A mixture of 200 ml of degassed water,20 g of potassium carbonate, 150 ml of 1,2-dimethoxyethane, 0.5 g ofPd(PPh₃)₄, 0.05 mol of 2-chloro-5-trifluoromethylpyridine and 0.05 molof 4-fluorophenylboronic acid was refluxed (80-90° C.) for 16-30 h. Theresulting reaction mixture was diluted with 300 ml of water andextracted with CH₂Cl₂ (2×100 ml). The combined organic layers were driedover MgSO₄, and the solvent removed by vacuum. The liquid products werepurified by fractional vacuum distillation. The solid materials wererecrystallized from hexane. The typical purity of isolated materials was>98%.

Iridium Complex:

A mixture of IrCl₃.nH₂O (54% Ir; 508 mg),2-(4-fluorophenyl)-5-trifluoromethylpyridine, from above (2.20 g),AgOCOCF₃ (1.01 g), and water (1 mL) was vigorously stirred under a flowof N₂ as the temperature was slowly (30 min) brought up to 185° C. (oilbath). After 2 hours at 185-190° C. the mixture solidified. The mixturewas cooled down to room temperature. The solids were extracted withdichloromethane until the extracts decolorized. The combineddichloromethane solutions were filtered through a short silica columnand evaporated. After methanol (50 mL) was added to the residue theflask was kept at −10° C. overnight. The yellow precipitate of thetris-cyclometalated complex, compound b, was separated, washed withmethanol, and dried under vacuum. Yield: 1.07 g (82%). X-Ray qualitycrystals of the complex were obtained by slowly cooling its warmsolution in 1,2-dichloroethane.

Iridium complex I(c) was made using an analogous procedure.

Example 19

This example illustrates the preparation of an iridiumelectroluminescent complex, shown as Formula I(d) in FIG. 3.

Ligand, 2-(2-thienyl)-5-(trifluoromethyl)pyridine

2-thienylboronic acid (Lancaster Synthesis, Inc., 1.00 g, 7.81 mmol),2-chloro-5-trifluoromethylpyrdine (Adrich Chemical Co., 1.417 g, 7.81mmol), tetrakistriphenylphosphine palladium(0) (Aldrich, 451 mg, 0.391mmol), potassium carbonate (EM Science, 3.24 g, 23.4 mmol), water (20mL), and dimethoxyethane (Aldrich 20 mL) were allowed to stir at refluxfor 20 hours under N₂, after which time the mixture was cooled to roomtemperature and the organic and aqueous layers were separated. Theaqueous layer was extracted with 3×50 mL of diethyl ether, and thecombined organic fractions were dried with sodium sulfate, filtered, andthe filtrate was evaporated to dryness. The crude product was purifiedby silica gel flash chromatography with CH₂Cl₂/hexanes (1:1) as theeluent (product Rf=0.5), to afford the product as a white crystallinesolid (yield=5.2 g, 73% isolated yield). ¹H NMR (CDCl₃, 296 K, 300 MHz):δ=7.73-7.57 (2H, m), 7.55 (1H, d. J=8.5 Hz), 7.34 (1H, d, J=4.8 Hz),6.88 (1H, d, J=4.8 Hz) ppm. ¹⁹F NMR (CDCl₃, 296K, 282 MHz) δ=−62.78 ppm.Intermediate bridged dimer,

[IrCl{2-(2-thienyl)-5-(trifluoromethyl)pyridine}2]2

2-(2-thienyl)-5-(trifluoromethyl)pyridine from above (555 mg, 2.42mmol), iridium trichloride (Strem Chemicals, 401 mg, 1.13 mmol),2-ethoxyethanol (Aldrich Chemical Co., 10 mL) and water (1 mL) wereallowed to reflux under nitrogen for 15 hours, after which time thereaction was allowed to cool to room temperature. The resultingprecipitated product was collected by filtration, washed with hexanes,and dried in vacuo, to afford 575 mg (37%) of the product as ared-orange solid. ¹H NMR (CDCl₃, 296 K, 300 MHz): δ=9.30 (4H, d, J=1.5Hz), 7.80 (4H, dd, J=2.0 Hz and 8.5 Hz), 7.59 (4H, d, J=8.5 Hz), 7.21(8H, d, J=4.8 Hz), 5.81 (d, 4H, J=4.9 Hz). ¹⁹F NMR (CDCl₃, 296K, 282MHz) δ=−62.07 ppm.

Iridium complex [Ir{2-(2-thienyl)-5-(trifluoromethyl)pyridine}₃]

[IrCl{2-(2-thienyl)-5-(trifluoromethyl)pyridine}₂]₂ from above (100 mg,0.073 mmol), 2-(2-thienyl)-5-(trifluoromethyl)pyridine from Example 1(201 mg, 0.88 mmol), and silver trifluoroacetate (Aldrich, 40 mg, 0.18mmol) were combined and allowed to stir at 170-180° C. under nitrogenfor 10 min. Then the mixture was allowed to cool to room temperature andit was redissolved in a minimum amount dichloromethane. The solution waspassed through a silica gel column with dichloromethane/hexanes (1:1) asthe eluting solvent. The first red-orange fraction to come down thecolumn (product Rf=0.5) was collected and evaporated to dryness. Theresidue was suspended in hexanes, and the precipiated product wasfiltered and washed with excess hexanes to remove any residual2-(2-thienyl)-5-(trifluoromethyl)pyridine, to afford the product as ared-orange solid. Isolated yield ≈50 mg (39%), ¹H NMR (CDCl₃, 296 K, 300MHz): δ=7.73-7.57 (6H, m), 7.55 (3H, d, J=8.5 Hz), 7.34 (3H, d, J=4.8Hz), 6.88 (3H, d, J=4.8 Hz). ¹⁹F NMR (CDCl₃, 296K, 282 MHz) δ=−62.78.

Example 20

This example illustrates the formation of OLEDs using the chargetransport compositions of the invention.

Thin film OLED devices including a hole transport layer (HT layer),electroluminescent layer (EL layer) and at least one electron transportand/or anti-quenching layer (ET/AQ layer) were fabricated by the thermalevaporation technique. The base vacuum for all of the thin filmdeposition was in the range of 10⁻⁶ torr. The deposition chamber wascapable of depositing five different films without the need to break upthe vacuum.

Patterned indium tin oxide (ITO) coated glass substrates from Thin FilmDevices, Inc were used. These ITO's are based on Corning 1737 glasscoated with 1400 Å ITO coating, with sheet resistance of 30 ohms/squareand 80% light transmission. The patterned ITO substrates were thencleaned ultrasonically in aqueous detergent solution. The substrateswere then rinsed with distilled water, followed by isopropanol, and thendegreased in toluene vapor for ˜3 hours.

The cleaned, patterned ITO substrate was then loaded into the vacuumchamber and the chamber was pumped down to 10⁻⁶ torr. The substrate wasthen further cleaned using an oxygen plasma for about 5-10 minutes.After cleaning, multiple layers of thin films were then depositedsequentially onto the substrate by thermal evaporation. Finally,patterned metal electrodes of Al or LiF and Al were deposited through amask. The thickness of the film was measured during deposition using aquartz crystal monitor (Sycon STC-200). All film thickness reported inthe Examples are nominal, calculated assuming the density of thematerial deposited to be one. The completed OLED device was then takenout of the vacuum chamber and characterized immediately withoutencapsulation.

The OLED samples were characterized by measuring their (1)current-voltage (I-V) curves, (2) electroluminescence radiance versusvoltage, and (3) electroluminescence spectra versus voltage. Theapparatus used, 200, is shown in FIG. 14. The I-V curves of an OLEDsample, 220, were measured with a Keithley Source-Measurement Unit Model237, 280. The electroluminescence radiance (in the unit of Cd/m²) vs.voltage was measured with a Minolta LS-110 luminescence meter, 210,while the voltage was scanned using the Keithley SMU. Theelectroluminescence spectrum was obtained by collecting light using apair of lenses, 230, through an electronic shutter, 240, dispersedthrough a spectrograph, 250, and then measured with a diode arraydetector, 260. All three measurements were performed at the same timeand controlled by a computer, 270. The efficiency of the device atcertain voltage is determined by dividing the electroluminescenceradiance of the LED by the current density needed to run the device. Theunit is in cd/A.

Iridium compounds XII(b) was made according to the procedure in Appl.Phys. Lett., 1999, 75, 4. The different iridium complexes have theproperties given below in Table 2. TABLE 2 Properties of the Iridiumcompounds HOMO vs Absorption LUMO vs E_(1/2) vs vacuum onset vacuum ELSCE, (eV), E_(1/2) vs (nm); (eV), Compound volt E4 SCE, volt E2-E4 E2I(a) 1.23 −6.07 −1.68 510 −3.64 I(b) 0.72 −5.56 −2.21 511 −3.13 I(c)1.17 −6.01 −1.62 539.5 −3.71 I(d) 1.05 −5.89 −1.74 571 −3.72

A summary of the device layers and thicknesses is given in Table 3. Inall cases the anode was ITO, as discussed above, the HT layer was MPMP,and the cathode was Al having a thickness in the range of 600-800 Å. Insome cases, a second ET layer 150 was present. This layer comprisedeither tris(8-hydroxyquinolato)aluminum(III), Alq, orbis(2-methyl-8-quinolinolato)(para-phenyl-phenolato)aluminum(III), BAlq,as indicated.

Comparative examples, a-d, where no ET/AQ layer were used in the deviceswere also prepared. These comparative examples demonstrate it isnecessary to use ET/AQ layer to achieve good device performance.

Comparative example a2 uses benzophenone as the ET/AQ layer, whichyields very poor device performance. Benzophenone is white in color andhas a band gap larger than that of EL compound I(a), which is yellow incolor. This example demonstrates it is not sufficient to use a largerband gap material in the ET/AQ layer to block energy transfer.

Comparative examples a3 and a4 use compound I(c) as the ET/AQ layer, andeither AlQ or BAlQ as the second electron transport layer. Relativelygood device performance was obtained in spite of the fact that compoundI(c) is orange in color which has a band gap smaller than that ofcompound I(a), which is yellow in color. TABLE 3 SAMPLE HT, Å EL, ÅET/AQ, Å ET, Å Comparative a 523 I(a) 520 9-1 506 I(a) II(b) 430 405 9-2507 I(b) Comp. A 407 408 9-3 507 I(a) Comp. B 405 407 9-4 505 I(a) II(a)404 305 9-5 515 I(a) II(c) 407 409 9-6 508 I(a) II(h) 411 416 9-7 510I(a) II(i) 408 412 9-8 516 I(a) II(d) 419 406 9-9 512 I(a) II(g) 434 4159-10 505 I(a) II(e) 415 432 9-11 514 I(a) II(f) 402 431 9-12 545 I(a)V(a) Alq 430 403 430 9-13 508 I(a) V(b) 625 425 9-14 509 I(a) V(c) 413416 9-15 578 I(a) V(d) 411 381 9-16 549 I(a) V(g) 425 423 9-17 533 I(a)VI(a) 417 411 9-18 527 I(a) V(e) 418 418 9-19 502 I(a) V(f) Alq 303 403106 9-20 505 I(a) V(k) 412 439 9-21 514 I(a) V(i) 416 408 9-22 513 I(a)V(h) 409 414 9-23 515 I(a) V(r) 500 410 9-24 516 I(a) V(l) 409 432 9-25504 I(a) V(j) 412 402 Comparative 507 I(a) Benzophenone a2 409 408Comparative 519 I(a) I(c) Alq 309 a3 411 110 Comparative 507 I(a) I(c)BAlq 308 a4 413 105 Comparative b 531 I(b) 500 9-26 512 I(b) Comp. A 410406 9-27 523 I(b) Comp. B 402 416 Comparative c 510 I(c) 532 9-28 512I(c) II(g) 415 414 9-29 516 I(c) II(b) 401 408 9-30 512 I(c) Comp. B 413407 9-31 545 I(c) Comp. A Alq 319 462 111 9-32 506 I(c) II(d) 403 4729-33 503 I(c) Comp. A 404 406 Comparative d 511 I(d) 508 9-34 504 I(d)Comp. B 411 418 9-35 511 I(d) II(d) 418 407 9-36 512 I(d) II(g) 404 4029-37 509 I(d) II(b) 409 409 9-38 516 I(d) II(a) 411 406

The devices were tested as described above and the results are given inTable 4 below. TABLE 4 APPROXIMATE PEAK PEAK PEAK RADIANCE EFFICIENCYWAVELENGTHS SAMPLE cd/m² cd/A nm Comparative a 4 0.01 525 at 21 V 9-13500 17 525 at 19 V 9-2 3000 10 525 at 22 V 9-3 4500 20 525 at 19 V 9-43500 11 525 at 20 V 9-5 1200 6 525 at 25 V 9-6 1900 at 8 525 24 V 9-71600 8.5 525 at 28 V 9-8 2200 16 525 at 25 V 9-9 400 11 525 at 21 V 9-101000 6 525 at 23 V 9-11 900 8.5 525 at 27 V 9-12 2300 5.4 525 at 20 V9-13 2700 10 525 at 27 V 9-14 400 10 525 at 15 V 9-15 90 4.4 525 at 22 V9-16 2000 13 525 at 23 V 9-17 80 0.01 525 at 20 V 9-18 200 1.1 525 at 22V 9-19 7000 30 525 at 15 V 9-20 1600 11 525 at 22 V 9-21 300 2.6 525 at19 V 9-22 1200 9.5 525 at 20 V 9-23 220 2.6 525 at 26 V 9-24 100 1.2 525at 22 V 9-25 180 8.5 525 at 25 V Comparative 16 0.2 525 a2 at 21 VComparative 3000 7 525 a3 at 22 V Comparative 750 7 525 a4 at 22 VComparative b 160 0.1 522 at 20 V 9-26 700 4 522 at 24 V 9-27 130 1.8522 at 24 V Comparative c 30 0.1 560 at 15 V 9-28 2400 13 560 at 23 V9-29 1400 6.5 560 at 20 V 9-30 2200 5.8 560 at 18 V 9-31 510 2.2 560 at20 V 9-32 1700 10 560 at 22 V 9-33 2000 5 560 at 27 V Comparative d 0.10.015 at 20 V 9-34 190 1.5 570 at 26 V 9-35 30 1.1 570 at 26 V 9-36 2002 570 at 24 V 9-37 50 0.8 570 at 25 V 9-38 430 2.5 570 at 25 V

The peak efficiency is the best indication of the value of theelectroluminescent compound in a device. It gives a measure of how manyelectrons have to be input into a device in order to get a certainnumber of photons out (radiance). It is a fundamentally importantnumber, which reflects the intrinsic efficiency of the light-emittingmaterial. It is also important for practical applications, since higherefficiency means that fewer electrons are needed in order to achieve thesame radiance, which in turn means lower power consumption. Higherefficiency devices also tend to have longer lifetimes, since a higherproportion of injected electrons are converted to photons, instead ofgenerating heat or causing an undesirable chemical side reactions.

As can be seen in the comparative examples of Table 4, devices madewithout the ET/AQ layer have much lower electroluminescence efficiencythan devices made with the ET/AQ layer. Also, for a given photoactivematerial, different device efficiency can be obtained with differentET/AQ materials, although all of these ET/AQ materials have band gaplarger than the energy of the luminescent exciton. This shows that toprevent the quenching of the luminescent exciton, it is not sufficientjust to block the energy transfer process. The electron transfer processalso has to be blocked. This is done via method outlined in criteria1-4. Therefore to obtain a maximal electroluminescence efficiency, thereexists at least one optimal, matched ET/AQ material for each differentelectroluminescent material as shown in Table 4.

As examples, the dependence of electroluminescence efficiency on theLUMO energies of the ET/AQ compounds are plotted in FIG. 15 and FIG. 16for emitters I(c) and I(d), respectively. For each photoactive material,the efficiency is quite sensitive to the ET/AQ compound used and anoptimal ET/AQ compound can be found by tuning the ET/AQ LUMO energy.FIG. 17 plots the best ET/AQ compound for all the emitters studied here.As can be seen there is a general correlation between the LUMO of theET/AQ compound and the LUMO of the emitter, within experimentaluncertainty. As the emitter LUMO energy decreases, there is acorresponding decrease in the LUMO energy of the best ET/AQ material.FIG. 18 plots the LUMO of the best ET/AQ compound (y) vs. the LUMO ofthe corresponding emitter (x). The data can be roughly fitted with alinear equation of y=2(±0.1)+0.273·x

1. A photoactive electronic device comprising: (a) an anode, (b) a cathode, said cathode having a work function energy level E₃; (c) a photoactive layer positioned between said anode and said cathode, said photoactive layer comprising a cyclometalated complex of a transition metal, said cyclometalated complex having a LUMO energy level E₂ and a HOMO energy level E₄; and (d) an electron transport and/or anti-quenching layer positioned between said cathode and said photoactive layer, said electron transport and/or anti-quenching layer having a LUMO energy level E₁ and a HOMO energy level E₅, with the proviso that: E ₁ −E ₃<1V,  (1) E ₁ −E ₂>−1V, and  (2) E ₄ −E ₅>−1V.  (4)
 2. The device of claim 1 wherein E₁−E₂>0.
 3. The device of claim 1 wherein E₄−E₅>0.
 4. The device of claim 1 wherein said electron transport and/or anti-quenching layer has an electron mobility of at least 10⁻⁷ cm²/(V·sec).
 5. The device of claim 1 wherein the electron transport and/or anti-quenching layer comprises a phenanthroline derivative.
 6. The device of claim 5 wherein the phenanthroline derivative has Formula II, wherein:

R¹ and R² are the same or different at each occurrence and are selected from H, F, Cl, Br, alkyl, heteroalkyl, alkenyl, alkynyl, aryl, heteroaryl, C_(n)H_(a)F_(b), OC_(n)H_(a)F_(b), C₆H_(c)F_(d), and OC₆H_(c)F_(d); a, b, c, and d are 0 or an integer such that a+b=2n+1 and c+d=5; n is an integer; x is 0 or an integer from 1 through 3; and y is 0, 1 or 2; with the proviso that there is at least one substituent on an aromatic group selected from F, C_(n)H_(a)F_(b), OC_(n)H_(a)F_(b), C₆H_(c)F_(d), and OC₆H_(c)F_(d).
 7. The device of claim 6, wherein n is an integer from 1 through
 12. 8. The device of claim 5 wherein the phenanthroline derivative is selected from Formulae II(a) through II(i) in FIG.
 5. 9. The device of claim 5 wherein the phenanthroline derivative has Formula III(a), wherein:

R¹ and R² are the same or different at each occurrence and are selected from H, F, Cl, Br, alkyl, heteroalkyl, alkenyl, alkynyl, aryl, heteroaryl, C_(n)H_(a)F_(b), OC_(n)H_(a)F_(b), C₆H_(c)F_(d), and OC₆H_(c)F_(d); R³ is the same or different at each occurrence and is selected from a single bond and a group selected from alkylene, heteroalkylene, arylene, heteroarylene, arylenealkylene, and heteroarylenealkylene; Q is selected from a single bond and a multivalent group; m is an integer equal to at least 2; p is 0 or 1; and x is 0 or an integer from 1 through
 3. 10. The device of claim 9, wherein: m is an integer from 2 through 10; n is in integer from 1 through 12; and with the proviso that when Q is a single bond, p is
 0. 11. The device of claim 5, wherein the phenanthroline derivative has Formula III(b), wherein:

R¹ and R² are the same or different at each occurrence and are selected from H, F, Cl, Br, alkyl, heteroalkyl, alkenyl, alkynyl, aryl, heteroaryl, C_(n)H_(a)F_(b), OC_(n)H_(a)F_(b), C₆H_(c)F_(d), and OC₆H_(c)F_(d); R³ is the same or different at each occurrence and is selected from a single bond and a group selected from alkylene, heteroalkylene, arylene, heteroarylene, arylenealkylene, and heteroarylenealkylene; Q is selected from a single bond and a multivalent group; m is an integer equal to at least 2; p is 0 or 1; and x is 0 or an integer from 1 through
 3. 12. The device of claim 5, wherein the device is a light-emitting diode, a light-emitting electrochemical cell, or a photodetector. 